Why still no dive acceleration difference?

[BlackBerry]

This is NACA16 airfoil 3-blade vs 4-blade efficiency compare at 0.4 Mach.

Obviously, 4-blade NACA16 outperforms 3-blade NACA16 WITHIN Vmax. There is 8% difference. What's the meaning of 8% efficieny for a 2000HP engine? 160HP!

What's the 18lbs spitfireXIV and 21lbs spitfire XIV Griffon 65 engine difference? （2220HP-2050）*85%=145HP!
What RAF did in order to achieve 21 lbs boost with spitfire XiV? Gear midification, 150 octane fuel, and so on.

4vs3.jpg

But there is only 2% difference between 3-blade and 4-blade RAF6/ClarkY.
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So NACA16 shows its outstanding/distinct character WITHIN envelope/Vmax.

RAF6, ClarkY and Gottingen airfoils are all conventional and of WWI peroid when biplanes dominated the sky. NACA16 was developed after 1939, new airfoil. And NACA16's advantage is NOT directly outperforms conventional airfoil in 3 blade configuration, its benefit only available when you add the fourth blade. There are two benifit:

1)Within Vmax. With the 4th blade, naca16 get 8% more efficiency while RAF6/ClarkY/Gotingen get 0% even negative.

2)above Vmax, with the 4th blade, naca16 could maintain stable efficiency（drops slightly） when advance ratio reaches 3.0. Those conventional airfoils usually in 3-blade configuration, and a 3-blade propeller efficiency drops sharply when advance ratio=3.